METHACRYLIC ACID

OSHA comments from the January 19, 1989 Final Rule on Air Contaminants Project extracted from 54FR2332 et. seq. This rule was remanded by the U.S. Circuit Court of Appeals and the limits are not currently in force.

CAS: 79-41-4; Chemical Formula: CH₂=C(CH₃)COOH

OSHA formerly had no limit for methacrylic acid. The ACGIH has a TLV-TWA of 20 ppm for this substance. Methacrylic acid is a liquid with an acrid, disagreeable odor. The proposed PEL was 20 ppm, and NIOSH (Ex. 8-47, Table N1) concurred that this limit is appropriate. The final rule establishes an 8-hour TWA PEL of 20 ppm for methacrylic acid, with a skin notation.

The primary toxic hazard associated with exposure to methacrylic acid is irritation, although the degree of irritation from exposure to this substance is significantly less than that from acrylic acid (ACGIH 1986/Ex. 1-3, p. 362).

Direct contact of methacrylic acid with the skin or eye can cause corrosion of the skin or blindness. In rabbits, the skin absorption LD(50) for methacrylic acid is 0.5 to 1 g/kg (Dow Chemical Company 1977m, as cited in ACGIH 1986/Ex. 1-3, p. 362). Rats exposed by inhalation to approximately 1000 ppm methacrylic acid exhibited eye irritation (Dow Chemical Company 1977m, as cited in ACGIH 1986/Ex. 1-3, p. 362). Rats exposed to 300 ppm for six hours daily for 20 days showed slight congestion of the kidneys (Gage 1970/Ex. 1-318).

Medical reports of acute exposures (at concentrations of up to 113 ppm) in an industrial setting revealed no respiratory symptoms; however, skin responses and a severe corneal burn were reported (Dow Chemical Company 1977m, as cited in ACGIH 1986/Ex. 1-3, p. 362). Only NIOSH commented on this substance.

In the final rule, OSHA is establishing a PEL of 20 ppm as an 8-hour TWA for this substance, with a skin notation. The Agency concludes that this limit will protect workers from the significant risk of severe eye and skin irritation, which are material health impairments that are associated with exposure to methacrylic acid at levels above the new limit. The skin notation is necessary to prevent dermal absorption and systemic toxicity.